The present invention generally relates to pneumatic tires, and in particular, to construction of ply tires with belt plies.
Typically, tires are manufactured from a single or multiply carcass of substantially U-shaped section having metal beads at the inner perimeters of the walls. Support can be provided to a tire carcass by steel cord belt plies extending around the outer periphery of the carcass and across the width of the tread. Such steel belt plies are relatively inextensible in the intended direction of rotation of the tire and include steel belt cords disposed parallel to that direction or at a low angle thereto. The belt plies act to restrict the movement of the tread and give the tire better road-holding properties. Support such as this type is particularly important in a radial tire, where the carcass is formed from a rubberized woven fabric having relatively inextensible reinforcing cords running transversely, i.e. radially, from bead to bead.
Technical difficulties have been encountered in incorporating steel belts into the tread area of the tire. One of the difficulties lies in ensuring good adhesion between the steel and the rubber. The centrifugal force of the steel belts can cause difficulty in the adhesion of the belt within the tire. Additionally, movement of the steel belts at higher speeds tends to create excessive temperatures in the tire, which can cause tread failure and delamination. The problem of delamination is particularly noticeable in the shoulder area of the tire.
One solution of the problem previously used by tire manufactures is to use a layer of calendared fabric laid circumferentially over the belt. This calendared fabric can also be used with wide fabric strips placed over the shoulder area of the tire, retaining the edges of the steel belt in a specific location of the tire. An example of this type of tire can be found in U.S. Pat. No. 4,284,117, issued to Poque et al. on 18 Aug. 1981. In order to cover the entire circumference of the tire and be retained in place, the prior art fabric must overlap itself across the width of tire at some location on the circumference. The overlapping area helps retain the prior art fabric around the circumference of the tire. However, because this type of overlapping adds weight, the potential length of the overlap is limited. A shorter overlap limits the length of the fabric and thereby the strength that the fabric can give to the tire. Additionally, the overlapping section of the fabric causes an uneven thickness of the fabric around the circumference.
To overcome this difficulty, a rubber tape was formed that had cords disposed longitudinally within the tape, and was wound around the belt plies and across the width of the tire. An example of this type of tire can be found in WO 2005/002883, filed by Pirelli Pneumatic S.P.A., and published on 13 Jan. 2005. The continuous nature of the tape provided greater strength. However, the longitudinal yarns were positioned in a spaced apart relationship by the rubber of the tape, which does not provide resistance to the separation of the yarns by items that probe at the area between the yarns.
Sowa et al. (EP 0131954) discloses a knitted fabric for use as tire reinforcement. “ . . . the knitting fabric is formed by arranging warps parallel to one another and twining a knitting yarn of a fine fiber around the warps to keep each space between the warps constant.” However, the Sowa patent warps cannot be kept exactly parallel and at the same spacing because the wefts are set “roughly on the warps to cross the warps at almost right angles without weaving and twining a knitting yarn of a fine fiber around the warps and wefts” (claim 2, lines 3-6). The fine fibers do not adequately fasten the adjacent warps together to hold them parallel and at the correct spacing and would fray if cut. Knitting yarn 22 of FIG. 3 connects adjacent warp yarns, but is too loose to hold spacing constant between the warp yarns. It would be desirable to have a knitted fabric that had the warps parallel and evenly spaced and that resisted fraying when cut for use in a tire cap ply.
Hence, as a solution to overcome the above difficulties, the present invention provides a pneumatic tire 100 comprising a tread 500, a carcass 200 having at least one belt ply 230 disposed below the tread 500, and a cap ply 300 located between the carcass 200 and the tread 500, wherein the cap ply comprises at least one layer of a weft inserted warp knit fabric tape 310 comprising an in-lay warp yarn set, a weft inserted yarn set, and a stitching yarn set, wherein the stitching yarn set forms a repeating stitch pattern on each warp yarn comprising a sequence of at least 2 stitches around the warp yarn from one stitching yarn and at least 2 stitches around the warp yarn from the adjacent stitching yarn, disposed in a flat helical pattern around the circumference of the carcass 200 in the area of at least one belt ply 230.